I have a cycle fitted with a NeoDrives X15 and the small battery in the head unit has failed. I have contacted NeoDrives, initially to ask about a problem with the time and here is their answer:
I wonder if any of you have managed to get similar items open by using heat and can tell me how much to use.There is an little Battery in the Display unit. This one is Empty, this is not causing a system fail but it can not remember the Time and date anymore. The only thing you can do is buying a new Display Unit or live with the issue. Some Customers have also successfully tried to go to an smartphone shop to let the change the little Batterie inside.
The case can be opend by Heat. But be carefull. Sometimes they brake while doing it. Phone shops do that vary well most of the time.